An anonymous reader quotes a report from The Guardian: Australian scientists have developed roof coatings that It can passively cool surfaces up to 6°C below ambient temperature.as well as extracting water from the atmosphere, which they say could reduce indoor temperatures during extreme heat events. A coating made from a porous film, which can be painted over existing roofs, works by reflecting 96% of incoming solar radiation, rather than absorbing the sun’s energy. It also has a high thermal emission, meaning it effectively dissipates heat to outer space when the sky is clear. Its properties are known as passive radiative cooling. […]
In one study, published in the journal Advanced Functional Materials, researchers tested a prototype for six months on the roof of the Sydney Nanoscience Hub, combining cold paint with a UV-resistant top layer that encouraged dew drops to roll into a receptacle. The scientists found that up to 390 milliliters per square meter per day could be collected for about a third of the year. Based on that water capture rate, an average Australian roof (about 200 square meters) could provide up to 70 liters on days favorable for dew collection, they estimate. […]
In well-insulated buildings, a 6°C decrease in roof temperature “could result in a smaller fraction of that cooling being reflected at the upper level of the house.” [said the study’s lead author, Prof Chiara Neto of the University of Sydney]but greater temperature reductions would be expected in most Australian homes, “where insulation is quite poor.” It said the cladding could also help reduce the urban heat island effect, where hard surfaces absorb more heat than natural surfaces, making urban centers between 1°C and 13°C warmer than rural areas. The researchers found that the prototype coating was composed of poly(vinylidene fluoride-co-hexafluoropropene), which is used in the construction industry but was “not a scalable technology in the future” due to its environmental concerns. However, they are now marketing a water-based paint that is similarly performing, affordable and safer for the environment, and costs about the same as standard premium paints.
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